1. Field of the Invention
This invention relates to a thermal recording apparatus for heat-sensitive recording materials of multiple colors and more particularly, to a thermal recording apparatus for heat-sensitive recording materials which can produce record images of different hues (color images) with a higher certainty and speed by decomposing with light in a substantially selective manner at least one coloring component in a predetermined unit between one thermal recording and the next thermal recording and a thermal recording head therefor which is small in size and low in cost.
2. Description of the Prior Art
Along with the rapid and remarkable development in the information industry, there has been aroused a demand for a method which can simply produce hard copies in color from such terminals of information system as computers or facsimiles. There have been proposed an ink jet system and a thermal transfer system in the prior art, but they are detrimental in one way or other. As ink containing color dyes are jetted from a small nozzle in the ink jet system, dyes or other ingredients tend to clog the nozzle, thereby reducing reliability of the record. On the other hand, as the ink sheets are heated and melted to be transferred image-wise to a sheet of paper in the thermal transfer system, it is necessary to use four ink sheets for obtaining, for example, a four color image. As the system requires a large number of ink sheets, it presents an economic disadvantage. Moreover, both systems require constant attention of an operator; he should watch the process carefully so as to replenish ink or ink sheets in time. As a result, both systems force complex and troublesome procedures in maintenance.
On the other hand, the thermal color system has been known as an alternative system which requires no such troublesome maintenance procedures, is highly reliable and widely used in black-and-white facsimile terminals and printers in recent years. The system is simple in use as it employs characteristically a recording material which is coated with a layer having a coloring mechanism on a substrate. There has been felt a demand for application of the system in multiple color recording.
Application of the system in multi-color recording needs to incorporate coloring mechanisms in a number corresponding to the desired number of colors on a substrate and to control such coloring mechanisms respectively. Many efforts have been made but coloring control has not heretofore been satisfactory. For instance, Japanese Patent Publication No. 69/1974 discloses a recording material which uses in one heat-sensitive coloring layer two kinds of coloring components which present different hues at different temperatures. Japanese Patent Publication No. 11989/1976 and No. 133991/1977, and a Japanese Patent Laid-open No. 88135/1979 describe respectively recording material comprising high temperature heat-sensitive coloring layers and low temperature heat-sensitive coloring layers which are laminated consecutively on a substrate. Japanese Patent Publication No. 17866/1975 and No. 5791/1976 disclose a recording material which includes, in addition to the above mentioned high and low temperature thermal coloring layers, a decolorizer agent which has a decolorizing effect on the coloring component in the low temperature layer which corresponds to the imaged area of the high temperature layer when images are being formed. But these conventional multiple color heat-sensitive recording materials are not quite satisfactory because of difficultiies in one way or other.
For instance, when images of different hues are to be formed by the low- and high-temperature coloring methods by means of a recording material having one or two layers of thermal color developing, the tone of the images developed at high temperature tends to mix with that of the images developed at low temperature. The degree of mixture changes as the recording conditions such as temperature, humidity or type of printers change, presenting a problem in producing images with stable and constant color tones. Further, as an area of the temperature similar to that of temperature printing is generated in the periphery of the high temperature color development zone, the area around the high temperature images becomes the area which generates low temperature. These phenomena are generally called color run or a blur and present a factor detrimental to clear imaging. Although color mixing can be prevented in the recording material having a decolorizing mechanism, the problem of color run or blur still remain.